China on May 2 moved its giant rig Ocean-981 and escort vessels, including military ships, and aircraft to the area in the East Sea deep within Vietnam’s exclusive economic zone and continental shelf.

Its vessels, including marine surveillance boats and frigates, constantly fired water cannons at Vietnamese sailors aboard civilian boats on duty.

Secretary John Kerry protested against China's illegal actions in the East Sea (Photo:AP)

The US and other nations involved in maritime navigation in the region are deeply concerned about China’s aggressive action, Kerry told reporters prior to a US-Singapore strategic dialogue in Washington DC.

"We want to see a code of conduct, we want to see this resolved peacefully through the law of the sea, through arbitration, through any other means but not direct confrontation and aggressive action," Kerry said.

For his part, Singapore Foreign Minister Kasiviswanathan Shanmugam said ASEAN Foreign Ministers issued a statement on the East Sea tensions at their 24th meeting in Myanmar on May 10.

"We need a situation where parties resolve their disputes and their differences in a way that's acceptable to all," he said.

Six US senators issued a joint statement criticizing China’s stationing of its oil rig in the disputed waters and attacks on Vietnamese ships, describing its actions as ‘troubling’ in the region.

“These actions threaten the free flow of global commerce in a vital region," said the joint statement signed by Democratic Senators Robert Menendez of New Jersey, Ben Cardin of Maryland and Patrick Leahy of Vermont and Republicans Marco Rubio of Florida, Jim Risch of Idaho and John McCain of Arizona.